(a) Technical Field
The present invention relates to a fuel cell electrode and a method for manufacturing a membrane-electrode assembly (MEA) using the same. More particularly, it relates to a fuel cell electrode, which has increased physical and chemical durability, and a method for manufacturing a membrane-electrode assembly (MEA) using the same.
(b) Background Art
A fuel cell stack, which substantially generates electricity in a fuel cell system, typically has a structure in which several tens to several hundreds of unit cells, each comprising a membrane-electrode assembly (MEA) and a separator, are stacked together. The MEA usually is made up of a polymer electrolyte membrane, a negative electrode and a positive electrode, which are disposed on each of both sides of the polymer electrolyte membrane. The negative electrode (also known as a “hydrogen electrode”, “fuel electrode”, “anode”, or “oxidizing electrode) and the positive electrode (also known as an “air electrode”, “oxygen electrode”, “cathode”, or “reducing electrode”) are configured in such a manner that a catalyst layer which has platinum catalyst nanoparticles is formed on an electrode backing layer (e.g., carbon paper or carbon cloth).
Conventional methods for manufacturing membrane-electrode assemblies will be described below. As shown in FIG. 1, a catalyst slurry is coated, sprayed or painted on a gas diffusion layer to form an electrode, and the electrode is bonded to a polymer electrode membrane by thermal compression. Alternatively, as shown in FIG. 2, a catalyst slurry is coated, sprayed or painted directly on a polymer membrane and the resulting polymer membrane is bonded to a gas diffusion layer. As yet another method, as shown in FIG. 3, a catalyst slurry is coated, sprayed or painted on a release paper and transferred to a polymer membrane to form an electrode, and the electrode is bonded to a gas diffusion layer.
However, although applying the catalyst slurry on the gas diffusion layer advantageously forms pores, the associated manufacturing process is inconvenient, and thus it is not used in a commercial process.
Moreover, the method of directly forming the catalyst layer on the polymer membrane can manufacture small area electrodes but has difficulties in manufacturing large area electrodes due to deformation of the polymer membrane.
Furthermore, in the case of the method of forming the catalyst layer on the release paper and transferring the catalyst layer to the polymer membrane, the catalyst layer may be cracked according to the thickness of the catalyst layer, the content of a binder, and the type of the catalyst. Therefore, the catalyst layer may be lost during transfer to the polymer membrane. Moreover, after the catalyst layer is transferred to the polymer membrane, cracks may form in the catalyst layer thereby directly exposing the polymer membrane to a gas supply channel of the separator via the cracks, thus deteriorating the performance and durability of the fuel cell.
Another factor that deteriorates the durability of the manufactured MEAs is that the polymer electrolyte membrane is broken down due to chemical instability, which occurs in both operation and idle states of the fuel cell. More specifically, the breakdown of the polymer electrolyte membrane is directly caused by hydroxyl radicals (OH radicals) generated by hydrogen peroxide produced when oxygen or hydrogen permeates through the polymer membrane and by hydrogen peroxide produced during the reaction at the oxygen electrode. The thus generated hydroxyl radicals break down the functional group (e.g., —SO3H) at an end of the polymer electrolyte (binder) to deteriorate the conductivity of hydrogen ions, thereby deteriorating the performance of the fuel cell.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.